Substitution type tio2 semi-conductors



United States Patent Ofiice 3,033,907 Patented May 8, 1962 3,033,907 SUBSTITUTION TYPE TiO SEMICONDUCTORS Charles V. Rue, Tiilin, Ohio, assignor to Erie Resistor Corporation, Erie, Pa., a corporation of Pennsylvania No Drawing. Filed May 20, 1957, Ser. No. 660,075 2 Claims. (Cl. 136-5) techniques of mixing, forming tov shape and firing. For

thermo-electric purposes, an extruded rod is a convenient shape because the hot junction can be located at one end and the cold junction at the other end.

The resistivity and the thermo-electric force are structure sensitive properties dependent upon the previous thermal history. By heating the ceramics to a high temperature (e.g., 12001500 C.) and quenching in air or other coolant, the high temperature structure is frozen into the ceramics with the result that the resistivity is lowered by two or more decades (i.e., decreased by 10 10 10 ohms/cm?) and the thermo-electric force is decreased. However, the change in thermo-electric force is relatively slight compared to the decrease in resistance so that the power output obtained is much greater for the quenched ceramics.

At low percentages of the substituted ions, the resistance is high (e.g., 10 to 10 ohms/cm?) but as the percentage approaches /2% the resistance of the quenched ceramic drops to 10 or 10 ohms/cm. Additions above 1% do not drop the resistance; Throughout the range A to mol. percent, the quenched ceramic has resistance of less than half the non-quenched ceramic which means the power output can be much greater. For power applications, the range of to 5% is useful with the maximum power (.26 Watt at .34 volt for a couple 1" in diameter and 1" in length) being developed from a body having the composition 97 mol. percent TiO and 3% Nb O with a hot junction temperature of 922 C. and a cold junction temperature of 180 C.

The following are specific examples:

I: Mol percent TiO 95-9975 Nb O 5-.25

TiO 95-9915 Sb O 5-.25

III:

Ti0 95-9975 T3205 5- 225 The pentavalent ions are given as part of the oxides but it Will be understood that any other form may be used. Salts break down and free metal oxidizes at the firing temperature of the ceramic.

The greatest power output is obtained from the quenched bodies containing T102 and Nb O A greater voltage but higher resistance is obtained with quenched ing.

Other cations with valences of from plus 1 to plus 6 have been added without improving the characteristics. Nor was any improvement obtained by multiple additions of 'pentavalent ions such as Nb, Sb, Ta, V, to obtain complex bodies of three or more components.

The highest thermo-electric power and voltage were obtained from bodies of TiO and Nb O when coupled with a metal of high positive (such as Chromel) with the cold junction temperature raised to 180-200 C. The temperature co-efficient of resistivity is negative with the resistance dropping rapidly until the cold junction temperature reaches and levelling off at about 200 C. The thermo-electric voltage drops slowly to cold junction temperatures up to 400 C. with a result that maximum power output is obtained 'at about 200 C. The bodies are not subject to oxidation up to at least hot junction temperatures of 900 C. which permits high temperature operation.

The TiO Nb O bodies exhibit rectification properties up to temperatures of 400 C. For example at 200 C., a body of 99% TiO and 1% Nb O has a forward resistance of 1.6 10 and a back resistance of 1.9)(10 ohms/cmfi. A body of 98.5% TiO and 1 /2% Nb O at 300 C. has a forward resistance of 1.3 10 and a back resistance of. 1.9 10 ohms/cm.

What is claimed as new is:

l. A high temperature fired semi-conductor ceramic body consisting essentially of a host lattice of TiO into which is introduced a percentage of pentavalent ions selected from the group consisting of Nb, Ta, Sb in a mol percentage range from .25 to 5% of the TiO said body being fired at about 12001500 C. and quenched from a temperature in the region of its firing temperature and characterized by a reduction in resistance of several decades in magnitude as compared to unquenched bodies of the same composition and being further characterized by a thermo-electric force which is relatively slightly decreased as compared to said decrease in resistance so that the thermoelectric power output obtained is much greater for the quenched bodies.

2. A thermocouple comprising a thermoelectric ele ment composed of a high temperature fired semi-conductor body consisting essentially of a host lattice of T102 into which is introduced a percentage of pentavalent ions selected from the group consisting of Nb, Ta, Sb in a mol percentage range from .25 to 5% of the TiO said body being fired at about 1200-1500 C. and quenched from a temperature in the region of its tiring temperature and characterized by a thermoelectric force which is relatively slightly decreased as compared to said decrease in resistance so that the thermo-electric power output obtained is much greater for the quenched bodies.

References Cited in the file of this patent UNITED STATES PATENTS 2,272,330 Schupp Feb. 10, 1942 2,311,918 Wainer et a1. Feb. 23, 1943 2,331,444 Wainer Oct. 12, 1943 2,511,216 Miller June 13, 1950 2,530,255 Malek Nov. 14, 1950 2,563,307 Burnham et a1. Aug. 7, 1951 2,588,508 Findley Mar. 11, 1952 2,675,417 Heibel Apr. 13, 1954 2,692,212 Jenkins et a1. Oct. 19, 1954 2,748,250 Anrus May 29, 1956 2,886,682 Martin o May 12, 1959 FOREIGN PATENTS 165,585 Australia Oct. 12, 1955 OTHER REFERENCES Johnson et al.: J. Amer. Ceramic Soc., vol. 32, No. 12, December 1949 (pages 398-401). 

1. A HIGH TEMPERATURE FIRED SEMI-CONDUCTOR CERAMIC BODY CONSISTING ESSENTIALLY OF A HOST LATTICE OF TIO2 INTO WHICH IS INTRODUCED A PERCENTAGE OF PENTAVALENT IONS SELECTED FROM THE GROUP CONSISTING OF NB, TA, SB IN A MOL PERCENTAGE RANGE FROM .25 TO 5% OF THE TIO2, SAID BODY BEING FIRED AT ABOUT 1200*-1500* C. AND QUENCHED FROM A TEMPERATURE IN THE REGION OF ITS FIRING TEMPERATURE AND CHARACTERIZED BY A REDUCTION IN RESISTANCE OF SEVERAL DECADES IN MAGNITUDE AS COMPARED TO UNQUENCHED BODIES OF THE SAME COMPOSITION AND BEING FURTHER CHARACTERIZED BY A THERMO-ELECTRIC FORCE WHICH IS RELATIVELY SLIGHTLY DECREASED AS COMPARED TO SAID DECREASE IN RESISTANCE SO THAT THE THERMOELECTRIC POWER OUTPUT OBTAINED IS MUCH GREATTER FOR THE QUENCHED BODIES. 